High-performance polyimides are presently employed in a number of applications, for example in joining metals to metals, and in joining metals to composite structures in the aerospace industry. In addition, polyimides are rapidly finding new uses as foam insulation in cryogenic applications and as structural foam, having increased structural stiffness without large weight increases. Foams of various densities and thermal and mechanical properties are now being required for future reusable launch vehicles, maritime ships, and aircraft. Polyimide foam materials have a number of beneficial attributes in these applications, such as high temperature and solvent resistance, flame resistance, low smoke generation, high modulus and chemical and hot water resistance.
Most polymeric cellular solids do not perform well at cryogenic temperatures, are not chemically stable, and are not inherently flame retardant or thermally stable. One polyimide foam is TEEK H developed at NASA Langley Research Center. (U.S. Pat. Nos. 5,994,418; 6,084,000; 6,133,330; 6,180,746; 6,222,007; 6,235,803; and Williams et al. (2005), “Effects of cell structure and density on the properties of high performance polyimide foams,” Polymers for Advance Technologies, 16, 167-174, which are hereby incorporated by reference). TEEK polyimide foam performs well physically, thermally, chemically, and is flame retardant, but improvements are possible.
Improved thermal performance translates to less material required to achieve the same insulation performance, resulting in lighter vehicles. Improved foam materials that have increased thermal and acoustic insulation power with the same or less weight are needed for aerospace, maritime, and other uses.